Joint component manufacturing method

ABSTRACT

Provided is a joint component manufacturing method for reducing occurrence of burrs upon bonding between a first member having a hole and a second member having a shaft portion and firmly bonding both members. In the method for manufacturing a joint component 100, a hole-side weak press-fit portion 112 is formed at a hole 111 of a flat plate ring-shaped first member 110. Moreover, each of a shaft-side weak press-fit portion 122 and a shaft-side strong press-fit portion 124 is formed at a shaft portion 121 of a cylindrical second member 120. The hole-side weak press-fit portion 112 and the shaft-side weak press-fit portion 122 are defined by a first weak press-fit interference Lw1 formed thinner than a first strong press-fit interference Ls1. The shaft-side strong press-fit portion 124 is defined by a first strong press-fit interference Ls1 as the minimum necessary press-fit interference for electric resistance welding upon electric resistance welding between the hole 111 and the shaft portion 121.

TECHNICAL FIELD

The present invention relates to a joint component manufacturing methodfor joining a first member and a second member by fitting of a shaftportion of the second member in a hole of the first member.

BACKGROUND ART

Typically, there has been a joint component manufacturing method forjoining a first member and a second member by fitting of a shaft portionof the second member in a hole of the first member. For example, in apress-fit bonding structure disclosed in Patent Literature 1 below, aburr housing portion configured to house burrs generated uponpress-fitting is formed in the vicinity of an end portion of a bondinginterface at which a hole of a first member and a shaft portion of asecond member are fitted to each other.

CITATION LIST Patent Literature

PATENT LITERATURE 1: JP-A-2005-14064

SUMMARY OF THE INVENTION

However, in the press-fit bonding structure described in PatentLiterature 1 above, the burr housing portion is formed continuously tothe bonding interface at which the hole of the first member and theshaft portion of the second member are fitted to each other. Thus, thereare problems that bonding force between the first member and the secondmember is weakened and such bonding force is further decreased due to aclearance in the burr housing portion in a case where the amount ofburrs entering the burr housing portion is small.

The present invention has been made for coping with the above-describedproblems. An object of the present invention is to provide the followingjoint component manufacturing method. In the manufacturing method,occurrence of burrs upon bonding between a first member having a holeand a second member having a shaft portion can be reduced while bothmembers can be firmly bonded to each other.

In order to achieve the above-described object, an aspect of the presentinvention is a joint component manufacturing method for joining a firstmember and a second member by fitting of a shaft portion of the secondmember in a hole of the first member, the first member and the secondmember each including weak press-fit portions with a first weakpress-fit interference at tip end portions first fitted to each otherupon fitting between the hole and the shaft portion, and the firstmember or the second member including a strong press-fit portionprotruding with respect to the weak press-fit portions and having athicker first strong press-fit interference than the first weakpress-fit interference on a far side of the weak press-fit portions. Themethod includes: a first weak press-fit step of press-fitting the weakpress-fit portions of the first member and the second member to eachother; and a first strong press-fit step of press-fitting one of theweak press-fit portions of the first member and the second member andthe strong press-fit portion to each other in a state in which electricresistance heat is generated between the first member and the secondmember by applying a current.

Further, in order to achieve the above-described object, another aspectof the present invention is a joint component manufacturing method forjoining a first member and a second member by fitting of a shaft portionof the second member in a hole of the first member, the first member andthe second member each including, at tip end portions first fitted toeach other upon fitting between the hole and the shaft portion, weakpress-fit portions not contacting each other at the tip end portions andhaving a second weak press-fit interference with respect to each strongpress-fit portion formed to protrude to a far side of each tip endportion and each strong press-fit portion having a thicker second strongpress-fit interference than the second weak press-fit interference. Themethod includes: a second weak press-fit step of press-fitting each weakpress-fit portion and each strong press-fit portion of the first memberand the second member to each other; and a second strong press-fit stepof press-fitting the strong press-fit portions of the first member andthe second member to each other in a state in which electric resistanceheat is generated between the first member and the second member byapplying a current.

According to each aspect of the present invention configured asdescribed above, in the joint component manufacturing method, the holeof the first member and the shaft portion of the second member arebonded to each other by press-fitting with the first strong press-fitinterference and the second strong press-fit interference throughpress-fitting with the first weak press-fit interference and the secondweak press-fit interference. In this case, the first weak press-fitinterference and the second weak press-fit interference are, withrespect to the first strong press-fit interference and the second strongpress-fit interference, formed such that an overlapping thickness (i.e.,the press-fit interference) between both members is decreased. Thus,according to the joint component manufacturing method of the presentinvention, occurrence of burrs upon bonding between the first memberhaving the hole and the second member having the shaft portion can bereduced while close contact between both members without any clearancesand firm bonding between both members can be realized.

According to other aspect of the present invention, in the jointcomponent manufacturing method, the first weak press-fit interferenceand the second weak press-fit interference are formed to such anoverlapping thickness that no burrs are generated between the firstmember and the second member fitted to each other.

According to the other aspect of the present invention configured asdescribed above, in the joint component manufacturing method, the firstweak press-fit interference and the second weak press-fit interferenceare formed to such a thickness that no burrs are generated between thefirst member and the second member fitted to each other. Thus,occurrence of burrs upon bonding between the first member having thehole and the second member having the shaft portion can be moreeffectively reduced. In this case, the first weak press-fit interferenceand the second weak press-fit interference are set for each of thematerials, shapes, and press-fit conditions of the first member and thesecond member, and therefore, are obtained by experiment in advance.Note that a burr is one generated when part of the material forming thehole and/or the shaft portion is carved or extruded to the periphery ofan opening of the hole upon fitting between the hole and the shaftportion in a press-fit state.

According to other aspect of the present invention, in the jointcomponent manufacturing method, a guide portion having an inclinedsurface or a curved surface is formed at at least one corner portion ofthe tip end portions first fitted to each other upon fitting between thehole and the shaft portion.

According to the other aspect of the present invention configured asdescribed above, the guide portion having the inclined surface or thecurved surface is formed at at least one corner portion of the tip endportions first fitted to each other upon fitting between the hole andthe shaft portion. Thus, the shaft portion of the second member issmoothly guided to the hole of the first member, and is easily fitted inthe hole. Thus, occurrence of burrs can be more effectively reduced.

According to other aspect of the present invention, in the jointcomponent manufacturing method, the weak press-fit portion has agradually-changing portion of which the shape gradually changes withrespect to the strong press-fit portion.

According to the other aspect of the present invention configured asdescribed above, in the joint component manufacturing method, the weakpress-fit portion has the gradually-changing portion of which the shapegradually changes with respect to the strong press-fit portion. Thus,the shaft portion of the second member is smoothly guided to the hole ofthe first member, and is easily fitted in the hole. Thus, occurrence ofburrs can be more effectively reduced.

According to other aspect of the present invention, in the jointcomponent manufacturing method, at least one of the first member and thesecond member is, at the first weak press-fit step and the second weakpress-fit step, supported in a displaceable state in a directionperpendicular to a fitting direction.

According to the other aspect of the present invention configured asdescribed above, in the joint component manufacturing method, at leastone of the first member and the second member is, at the first weakpress-fit step and the second weak press-fit step, supported in thedisplaceable state in the direction perpendicular to the fittingdirection. Thus, even in a case where misalignment between the hole ofthe first member and the shaft portion of the second member hasoccurred, the first member and/or the second member are, at the firstweak press-fit step and the second weak press-fit step, moved to performfitting with the centers of both members being coincident with eachother. With this configuration, according to the joint componentmanufacturing method of the present invention, the first member and thesecond member can be bonded to each other with the cores of the firstmember and the second member being coincident with each other even in acase where the cores are shifted from each other upon bonding betweenboth members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of an outline configuration of ajoint component formed by a joint component manufacturing methodaccording to the present invention.

FIG. 2 is a flowchart of processing steps of a joint componentmanufacturing method according to a first embodiment of the presentinvention.

FIG. 3A and FIG. 3B each schematically illustrates a first member and asecond member used in the first embodiment of the present invention,FIG. 3A being a front sectional view of the first member and FIG. 3Bbeing a front sectional view of the second member.

FIG. 4 is a schematic sectional view of a main portion for describing amain portion configuration in a state in which the first member isarranged on the second member at one step of the joint componentmanufacturing method according to the first embodiment of the presentinvention.

FIG. 5 is a schematic sectional view of a processing machine used forthe joint component manufacturing method according to the firstembodiment of the present invention in a state in which the first memberand the second member are arranged on the processing machine.

FIG. 6 is a schematic sectional view of a main portion for describing amain portion configuration in a state right after a first weak press-fitstep as one step of the joint component manufacturing method accordingto the first embodiment of the present invention.

FIG. 7 is a schematic sectional view of a main portion for describing amain portion configuration in a state right after a first strongpress-fit step as one step of the joint component manufacturing methodaccording to the first embodiment of the present invention.

FIG. 8 is a flowchart of processing steps of a joint componentmanufacturing method according to a second embodiment of the presentinvention.

FIG. 9 is a schematic sectional view of a main portion for describing amain portion configuration in a state in which a first member isarranged on a second member at one step of the joint componentmanufacturing method according to the second embodiment of the presentinvention.

FIG. 10 is a schematic sectional view of a main portion for describing amain portion configuration in a state right after a second weakpress-fit step as one step of the joint component manufacturing methodaccording to the second embodiment of the present invention.

FIG. 11 is a schematic sectional view of a main portion for describing amain portion configuration in a state right after a second strongpress-fit step as one step of the joint component manufacturing methodaccording to the second embodiment of the present invention.

FIG. 12 is a schematic sectional view of a main portion for describing amain portion configuration in a state in which a first member isarranged on a second member at one step of a joint componentmanufacturing method according to a variation of the present invention.

FIG. 13 is a schematic sectional view of a main portion for describing amain portion configuration in a state in which a first member isarranged on a second member at one step of a joint componentmanufacturing method according to another variation of the presentinvention.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

Hereinafter, a first embodiment of a joint component manufacturingmethod according to the present invention will be described withreference to the drawings. FIG. 1 is a schematic sectional view of anoutline configuration of a joint component 100 formed by the jointcomponent manufacturing method according to the present invention.Moreover, FIG. 2 is a flowchart of the flow of main steps in the methodfor manufacturing the joint component 100 according to the firstembodiment of the present invention. Note that for the sake of easyunderstanding of the present invention, each figure referred in thepresent specification is schematically illustrated, and for example,some components are exaggeratingly illustrated. Thus, the dimensions andratio of each component may be changed.

First, the joint component 100 formed by the joint componentmanufacturing method according to the present invention will be brieflydescribed. The joint component 100 mainly includes a first member 110obtained in such a manner that a steel member is formed in a flat platering shape, and a second member 120 obtained in such a manner that asteel member is formed in a cylindrical shape. A though-hole-shaped hole111 to which the second member 120 is bonded with the second member 120being fitted in the hole 111 is formed at a center portion of a flatplate ring body of the first member 110. Moreover, a cylindrical shaftportion 121 bonded with the shaft portion 121 being fitted in the hole111 of the first member 110 is formed on one end side (the lower side asviewed in the figure) of a cylindrical body of the second member 120.The first member 110 and the second member 120 are, at the hole 111 andthe shaft portion 121, bonded to each other by electric resistancewelding to integrally form the joint component 100.

The joint component 100 includes, for example, a component forming apower transmission device such as a clutch or a transmission in aself-propelled vehicle, the component including, for example, a pulleyin a centrifugal clutch, an interlock sleeve in a manual transmission,or a manual plate in an automatic transmission.

First, a worker manufacturing the joint component 100 prepares, as afirst step, each of the first member 110 and the second member 120 asmaterials of the joint component 100, as illustrated in FIG. 3A and FIG.3B. The first member 110 and the second member 120 are formed bypunching using a press, bending using a press, or mechanical processingsuch as cutting. In this case, a hole-side weak press-fit portion 112and a shaft-side weak press-fit portion 122 are each formed at a bondingportion between the first member 110 and the second member 120, i.e.,the hole 111 and the shaft portion 121.

As illustrated in FIG. 4, the hole-side weak press-fit portion 112 andthe shaft-side weak press-fit portion 122 are portions formed with afirst weak press-fit interference Lw1 as a predetermined press-fitinterference at fitting tip end portions as tip end portions firstfitted to each other when the shaft portion 121 of the second member 120is fitted in the hole 111 of the first member 110. The first weakpress-fit interference Lw1 is the thickness of an overlapping portionupon fitting between the hole-side weak press-fit portion 112 and theshaft-side weak press-fit portion 122. The first weak press-fitinterference Lw1 is formed smaller (thinner) than a later-describedfirst strong press-fit interference Ls1.

More specifically, the first weak press-fit interference Lw1 is set tosuch a size that the amount of burrs generated when the shaft-side weakpress-fit portion 122 of the shaft portion 121 is press-fitted in thehole-side weak press-fit portion 112 of the hole 111 is less than theamount of burrs generated when at least a later-described shaft-sidestrong press-fit portion 124 is press-fitted in the hole-side weakpress-fit portion 112. The first weak press-fit interference Lw1 is setfor each of the materials, shapes, and press-fit conditions of the firstmember 110 and the second member 120, and therefore, is experimentallyobtained in advance.

In the present embodiment, the first weak press-fit interference Lw1 isset to such a size that no burrs due to radial compression anddeformation of at least one of the hole-side weak press-fit portion 112or the shaft-side weak press-fit portion 122 are generated when theshaft-side weak press-fit portion 122 is press-fitted in the hole-sideweak press-fit portion 112. Note that according to experiment by thepresent inventor et al., the first weak press-fit interference Lw1preferably has a diameter of greater than 0 mm and equal to or less than0.1 mm in a case where the diameter of each of the hole 111 and theshaft portion 121 formed of the steel members is within a range of 10 mmto 100 mm in terms of diameter.

The first weak press-fit interference Lw1 is defined by the minustolerance of the hole 111 with respect to a reference inner diameterdimension of the hole-side weak press-fit portion 112 and the plustolerance of the shaft portion 121 with respect to a reference outerdiameter dimension of the shaft-side weak press-fit portion 122. Thatis, the first weak press-fit interference Lw1 is defined by interferencefit between the hole 111 and the shaft portion 121. The formation lengthLwh of the shaft-side weak press-fit portion 122 on a side provided withthe shaft-side strong press-fit portion 124 among the hole-side weakpress-fit portion 112 and the shaft-side weak press-fit portion 122 isset in a relationship with the formation length Lsh of the shaft-sidestrong press-fit portion 124. That is, the formation length Lwh of theshaft-side weak press-fit portion 122 is a portion for reducing the burrgeneration amount due to fitting between the hole 111 and the shaftportion 121. On the other hand, the formation length Lsh of theshaft-side strong press-fit portion 124 is a portion defining bondingforce between the hole 111 and the shaft portion 121.

Thus, the formation length Lwh of the shaft-side weak press-fit portion122 is set according to the bonding force between the hole 111 and theshaft portion 121, the bonding force being necessary for the jointcomponent 100. According to the experiment by the present inventor etal., the formation length Lwh of the shaft-side weak press-fit portion122 may be preferably equal to or less than the half of the formationlength Lsh of the shaft-side strong press-fit portion 124, and morepreferably equal to or less than ⅓ of the formation length Lsh of theshaft-side strong press-fit portion 124. In the present embodiment, theformation length Lwh of the shaft-side weak press-fit portion 122 isformed equal to or less than ⅓ of the formation length Lsh of theshaft-side strong press-fit portion 124.

The lower limit of the formation length Lwh of the shaft-side weakpress-fit portion 122 is set to such a length that the hole-side weakpress-fit portion 112 and the shaft-side weak press-fit portion 122evenly contact each other in a cylindrical surface shape and smoothelectrical conduction between both portions is allowed. According to theexperiment by the present inventor et al., the lower limit of theformation length Lwh of the shaft-side weak press-fit portion 122 may beequal to or greater than ⅕ of the thickness ST of a bonding portionbetween the hole 111 and the shaft portion 121, and more preferablyequal to or less than ¼ of such a bonding portion.

On the other hand, the formation length Lwh of the hole-side weakpress-fit portion 112 not provided with the shaft-side strong press-fitportion 124 in the hole 111 is formed with a thickness of equal to orgreater than the thickness ST in bonding between the hole 111 and theshaft portion 121. In the present embodiment, the thickness ST inbonding between the hole 111 and the shaft portion 121 is the same asthe thickness of the first member 110, and therefore, the formationlength Lwh of the hole-side weak press-fit portion 112 is formed withthe same length as the thickness of the first member 110, i.e., isformed across the entirety of the hole 111.

A gradually-changing portion 123 is formed at a far-side back endportion (the lower side as viewed in the figure) of the shaft-side weakpress-fit portion 122. The gradually-changing portion 123 is a portionof which the shape gradually changes between the shaft-side weakpress-fit portion 122 and the shaft-side strong press-fit portion 124.In the present embodiment, the gradually-changing portion 123 is formedsuch that the shaft-side weak press-fit portion 122 and the shaft-sidestrong press-fit portion 124 are connected by an arc-shaped curvedsurface. The shaft-side strong press-fit portion 124 is formed on a farside (the lower side as viewed in the figure) of the gradually-changingportion 123.

The shaft-side strong press-fit portion 124 is a portion formed with thefirst strong press-fit interference Ls1 as a predetermined press-fitinterference from the hole-side weak press-fit portion 112. The firststrong press-fit interference Ls1 is the thickness of an overlappingportion upon fitting between the shaft-side strong press-fit portion 124and the hole-side weak press-fit portion 112. The first strong press-fitinterference Ls1 is formed greater (thicker) than the first weakpress-fit interference Lw1. More specifically, the first strongpress-fit interference Ls1 is set such that the minimum necessarypress-fit interference for electric resistance welding is ensured uponelectric resistance welding between the hole 111 and the shaft portion121.

The first strong press-fit interference Ls1 is set for each of thematerials, shapes, and press-fit conditions of the first member 110 andthe second member 120, and therefore, is experimentally obtained inadvance. According to the experiment by the present inventor et al., thefirst strong press-fit interference Ls1 preferably has a diameter of 0.5mm±0.05 mm in a case where the diameter of each of the hole 111 and theshaft portion 121 formed of the steel members is within a range of 10 mmto 100 mm in terms of diameter.

The first strong press-fit interference Ls1 is defined by the minustolerance of the hole 111 with respect to the reference inner diameterdimension of the hole-side weak press-fit portion 112 and the plustolerance of the shaft portion 121 with respect to the reference outerdiameter dimension of the shaft-side strong press-fit portion 124. Thatis, the first strong press-fit interference Ls1 is defined byinterference fit between the hole 111 and the shaft portion 121.Moreover, the formation length Lsh of the shaft-side strong press-fitportion 124 is set according to the bonding force between the hole 111and the shaft portion 121, the bonding force being necessary for thejoint component 100.

Next, the worker sets, as a second step, the first member 110 and thesecond member 120 on a processing machine 200 configured to performelectric resistance welding. The processing machine 200 described hereinis a welding device configured to generate electric resistance heat byapplying a current between two members fitted to each other to press-fitthese two members, thereby generating plastic flow of an interfacebetween these members to perform solid phase bonding of the members. Asillustrated in FIG. 5, the processing machine 200 mainly includes afirst die 201 and a second die 202.

The first die 201 and the second die 202 are components configured topress the hole 111 of the first member 110 and the shaft portion 121 ofthe second member 120 in a current application state to press-fit theseportions. Each of the first die 201 and the second die 202 is made of amaterial (e.g., chromium copper) exhibiting electric conductivity. Ofthese components, the first die 201 is a movable die configured to pressthe first member 110 arranged on the second member 120 toward the secondmember 120, and is formed in a cylindrical shape.

On the other hand, the second die 202 is a fixed die configured tosupport the second member 120, and is formed in a flat plate shape. Inthis case, a recessed portion 202 a recessed in a ring shape is formedat a portion of a surface of the second die 202 corresponding to anouter peripheral portion of the shaft portion 121 of the second member120. That is, the first die 201 and the second die 202 press both of thefirst member 110 and the second member 120 in a state in which each ofthe first member 110 and the second member 120 is not restricted in adirection perpendicular to a pressing direction, i.e., a radialdirection of each of the first member 110 and the second member 120, andis displaceable in such a direction.

At the second step, the worker arranges the second member 120 on thesecond die 202. Thereafter, the worker arranges the first member 110 onthe shaft portion 121 of the second member 120. In this case, for thefirst weak press-fit interference Lw1, the inner diameter of the hole111 is smaller than the outer diameter of the shaft portion 121 of thesecond member 120. Thus, the first member 110 is placed on the shaftportion 121 of the second member 120.

Next, the worker press-fits, as a third step, the hole-side weakpress-fit portion 112 of the first member 110 and the shaft-side weakpress-fit portion 122 of the second member 120 to each other.Specifically, the worker operates the processing machine 200 to move(move downward in a direction indicated by a dashed arrow in each ofFIGS. 4 and 5) the first die 201 toward the second die 202 in anon-current-application state. Accordingly, as illustrated in FIG. 6,the hole-side weak press-fit portion 112 of the hole 111 of the firstmember 110 is fitted in the shaft-side weak press-fit portion 122 of theshaft portion 121 of the second member 120. In this case, for the firstmember 110 and the second member 120, the first weak press-fitinterference Lw1 is set to such a thickness that no burrs are generatedbetween these members, and therefore, the first member 110 and thesecond member 120 are fitted to each other with no burrs between thesemembers.

Moreover, at the third step, the first die 201 and the second die 202each press the first member 110 and the second member 120 with thesemembers being displaceable in the radial direction. Thus, in a casewhere the positions of the center axes of the hole-side weak press-fitportion 112 and the shaft-side weak press-fit portion 122 are shiftedfrom each other upon fitting therebetween, at least one of the firstmember 110 or the second member 120 is displaced in the radial directionsuch that the positions of the center axes of these portions arecoincident with each other. In this manner, the first member 110 and thesecond member 120 are fitted to each other with the center axes beingcoincident with each other. The third step corresponds to a first weakpress-fit step according to the present invention. That is, each of thehole-side weak press-fit portion 112 and the shaft-side weak press-fitportion 122 corresponds to a weak press-fit portion according to thepresent invention.

Next, the worker press-fits, as a fourth step, the hole-side weakpress-fit portion 112 of the first member 110 and the shaft-side strongpress-fit portion 124 of the second member 120 to each other.Specifically, the worker operates the processing machine 200 to move(move downward in a direction indicated by a dashed arrow in FIG. 6) thefirst die 201 toward the second die 202 in a current application statebetween the first die 201 and the second die 202. Thus, as illustratedin FIG. 7, the hole-side weak press-fit portion 112 of the hole 111 ofthe first member 110 is fitted in the shaft-side strong press-fitportion 124 through the gradually-changing portion 123 of the shaftportion 121 of the second member 120. Then, solid phase bonding betweenthe hole-side weak press-fit portion 112 and the shaft-side strongpress-fit portion 124 is made by resistance heat by applying a currentand pressure due to lowering of the first die 201.

In this case, a bonding portion SP between the hole 111 and the shaftportion 121 is formed inclined from the shaft-side weak press-fitportion 122 toward the shaft-side strong press-fit portion 124. Further,a burr B due to solid phase bonding between the hole-side weak press-fitportion 112 and the shaft-side strong press-fit portion 124 might begenerated at a tip end portion of the bonding portion SP. That is, theburr B is or is not generated according to the formation length Lwh ofthe shaft-side weak press-fit portion 122.

At the bonding portion SP, a press-fit portion between the shaft-sideweak press-fit portion 122 and part (the upper side as viewed in FIGS. 4and 6) of the hole-side weak press-fit portion 112 is a bonding portionformed by press-fit bonding and/or solid phase bonding. A press-fitportion between the shaft-side strong press-fit portion 124 and anotherpart (the lower side as viewed in FIGS. 4 and 6) of the hole-side weakpress-fit portion 112 is a bonding portion formed by solid phasebonding. In this case, the press-fit portion between the shaft-side weakpress-fit portion 122 and part of the hole-side weak press-fit portion112 includes, according to the materials, shapes, press-fit conditions,and current application conditions of the first member 110 and thesecond member 120, the case of bonding only by press-fitting, the caseof bonding only by solid phase bonding, and the case of bonding by acombination of press-fit bonding and solid phase bonding. Thus,according to the joint component manufacturing method of the presentinvention, the formation length Lwh of the shaft-side weak press-fitportion 122 and the formation length Lsh of the shaft-side strongpress-fit portion 124 are adjusted as necessary so that the amount ofgenerated burrs B and bonding strength between both members can beadjusted.

By the fourth step, the first member 110 and the second member 120 arebonded to each other to form the joint component 100. The fourth stepcorresponds to a first strong press-fit step according to the presentinvention. That is, the shaft-side strong press-fit portion 124corresponds to a strong press-fit portion according to the presentinvention.

Note that the bonding portion SP does not clearly appear, and FIG. 7merely illustrates trend. Moreover, in the first embodiment, the workerinstructs the processing machine 200 to execute each of the third andfourth steps. However, the processing machine 200 can be configured tocontinuously execute the third step and the fourth step by a singleinstruction.

Next, the worker takes, as a fifth step, the joint component 100 out ofthe processing machine 200. Specifically, the worker confirms, after thefourth step, that the first die 201 has been separated (has moved upwardas viewed in the figure) from the second die 202 and the processingmachine 200 has returned to an original position, and then, takes thejoint component 100 out of the second die 202. Thereafter, the workerperforms necessary processing for the joint component 100, therebybringing the joint component 100 to completion. This post-processing forthe joint component 100 does not directly relate to the presentinvention, and therefore, description thereof will be omitted.

As seen from operation description above, in the method formanufacturing the joint component 100, the hole 111 of the first member110 and the shaft portion 121 of the second member 120 are, according tothe first embodiment, bonded to each other by press-fitting with thefirst strong press-fit interference Ls1 through press-fitting with thefirst weak press-fit interference Lw1. In the this case, the first weakpress-fit interference Lw1 is, with respect to the first strongpress-fit interference Ls1, formed such that an overlapping thickness(i.e., the press-fit interference) between both members is decreased.Thus, according to the method for manufacturing the joint component 100according to the present invention, occurrence of the burrs B in bondingbetween the first member 110 having the hole 111 and the second member120 having the shaft portion 121 is reduced while close contact betweenboth members without any clearances and firm bonding between bothmembers can be realized.

Further, implementation of the present invention is not limited to theabove-described embodiment, and various changes can be made withoutdeparting from the object of the present invention.

For example, in the above-described embodiment, the shaft-side strongpress-fit portion 124 as the strong press-fit portion according to thepresent invention is provided at the shaft portion 121 of the secondmember 120. However, the strong press-fit portion may be formed ateither one of the first member 110 or the second member 120. Thus, thestrong press-fit portion can be formed as a hole-side strong press-fitportion at the hole 111 of the first member 110 on a far side (the upperside as viewed in FIG. 4) of the hole-side weak press-fit portion 112.

Second Embodiment

Next, a second embodiment of a joint component manufacturing methodaccording to the present invention will be described with reference toFIGS. 8 to 11. In the second embodiment, differences from the firstembodiment will be mainly described.

A joint component 300 configured in a manner similar to that of thejoint component 100 mainly includes a first member 310 and a secondmember 320. In the first member 310, each of a hole-side weak press-fitportion 312, a gradually-changing portion 313, and a hole-side strongpress-fit portion 314 is formed at a through-hole-shaped hole 311.Moreover, the second member 320 is configured such that each of ashaft-side weak press-fit portion 322, a gradually-changing portion 323,and a shaft-side strong press-fit portion 324 is formed at a cylindricalshaft portion 321.

As illustrated in FIG. 9, the hole-side weak press-fit portion 312 andthe shaft-side weak press-fit portion 322 are portions formed with asecond weak press-fit interference Lw2 as a predetermined press-fitinterference at fitting tip end portions as tip end portions firstfitted to each other when the shaft portion 321 of the second member 320is fitted in the hole 311 of the first member 310. The second weakpress-fit interference Lw2 is the thickness of an overlapping portionupon fitting between the hole-side weak press-fit portion 312 and theshaft-side strong press-fit portion 324 and upon fitting between theshaft-side weak press-fit portion 322 and the hole-side strong press-fitportion 314. The second weak press-fit interference Lw2 is formedsmaller (thinner) than a later-described second strong press-fitinterference Ls2.

More specifically, as in the first weak press-fit interference Lw1, thesecond weak press-fit interference Lw2 is set to such a size that theamount of burrs generated when the shaft-side strong press-fit portion324 is press-fitted in the hole-side weak press-fit portion 312 and whenthe shaft-side weak press-fit portion 322 is press-fitted in thehole-side strong press-fit portion 314 is less than the amount of burrsgenerated when at least the later-described shaft-side strong press-fitportion 324 is press-fitted in the hole-side strong press-fit portion314. The second weak press-fit interference Lw2 is set for each of thematerials, shapes, and press-fit conditions of the first member 310 andthe second member 320, and therefore, is experimentally obtained inadvance. Moreover, the same second weak press-fit interference Lw2forming the hole-side weak press-fit portion 312 and the shaft-side weakpress-fit portion 322 is applied.

In the present embodiment, the second weak press-fit interference Lw2is, as in the first weak press-fit interference Lw1, set to such a sizethat no burrs are generated due to compression deformation of eachportion in a radial direction when the shaft-side strong press-fitportion 324 is press-fitted in the hole-side weak press-fit portion 312and when the shaft-side weak press-fit portion 322 is press-fitted inthe hole-side strong press-fit portion 314. Note that according toexperiment by the present inventor et al., the second weak press-fitinterference Lw2 preferably has a diameter of greater than 0 mm andequal to or less than 0.1 mm in a case where the diameter of each of thehole 311 and the shaft portion 321 formed of steel members is within arange of 10 mm to 100 mm in terms of diameter.

As in the first weak press-fit interference Lw1, the second weakpress-fit interference Lw2 is defined by interference fitting betweenthe hole 311 and the shaft portion 321. Moreover, as in the formationlength Lwh of the shaft-side weak press-fit portion 122, the formationlength Lwh of each of the hole-side weak press-fit portion 312 and theshaft-side weak press-fit portion 322 is set in a relationship with theformation length Lsh of each of the hole-side strong press-fit portion314 and the shaft-side strong press-fit portion 324. That is, theformation length Lwh of each of the hole-side weak press-fit portion 312and the shaft-side weak press-fit portion 322 is a portion for reducingthe amount of burrs generated due to fitting between the hole 311 andthe shaft portion 321. On the other hand, the formation length Lsh ofeach of the hole-side strong press-fit portion 314 and the shaft-sidestrong press-fit portion 324 is a portion defining bonding force betweenthe hole 311 and the shaft portion 321.

Thus, the formation length Lwh of each of the hole-side weak press-fitportion 312 and the shaft-side weak press-fit portion 322 is setaccording to the bonding force between the hole 311 and the shaftportion 321, the bonding force being necessary for the joint component300. According to the experiment by the present inventor et al., theformation length Lwh of each of the hole-side weak press-fit portion 312and the shaft-side weak press-fit portion 322 may be preferably equal toor less than the half of the formation length Lsh of each of thehole-side strong press-fit portion 314 and the shaft-side strongpress-fit portion 324, and more preferably equal to or less than ⅓ ofthe formation length Lsh of each of the hole-side strong press-fitportion 314 and the shaft-side strong press-fit portion 324. In thepresent embodiment, the formation length Lwh of each of the hole-sideweak press-fit portion 312 and the shaft-side weak press-fit portion 322is formed equal to or less than ⅓ of the formation length Lsh of each ofthe hole-side strong press-fit portion 314 and the shaft-side strongpress-fit portion 324.

The lower limit of the formation length Lwh of each of the hole-sideweak press-fit portion 312 and the shaft-side weak press-fit portion 322is set to such a length that the hole-side weak press-fit portion 312and the shaft-side strong press-fit portion 324 evenly contact eachother in a cylindrical surface shape, the hole-side strong press-fitportion 314 and the shaft-side weak press-fit portion 322 evenly contacteach other in a cylindrical surface shape, and smooth electricalconduction between both portions is allowed. According to the experimentby the present inventor et al., the lower limit of the formation lengthLwh of each of the hole-side weak press-fit portion 312 and theshaft-side weak press-fit portion 322 may be equal to or greater than ⅕of the thickness ST of a bonding portion between the hole 311 and theshaft portion 321, and more preferably equal to or greater than ¼ ofsuch a bonding portion.

The hole-side strong press-fit portion 314 and the shaft-side strongpress-fit portion 324 are portions formed with the second strongpress-fit interference Ls2 as a predetermined press-fit interferencebetween these portions. The second strong press-fit interference Ls2 isthe thickness of an overlapping portion upon fitting between thehole-side strong press-fit portion 314 and the shaft-side strongpress-fit portion 324. The second strong press-fit interference Ls2 isformed greater (thicker) than the second weak press-fit interferenceLw2. More specifically, the second strong press-fit interference Ls2 isset such that the minimum necessary press-fit interference for electricresistance welding is ensured upon electric resistance welding betweenthe hole 311 and the shaft portion 321.

The second strong press-fit interference Ls2 is set for each of thematerials, shapes, and press-fit conditions of the first member 310 andthe second member 320, and therefore, is experimentally obtained inadvance. According to the experiment by the present inventor et al., thesecond strong press-fit interference Ls2 preferably has a diameter of0.5 mm±0.05 mm in a case where the diameter of each of the hole 311 andthe shaft portion 321 formed of the steel members is within a range of10 mm to 100 mm in terms of diameter.

The second strong press-fit interference Ls2 is defined by interferencefitting between the hole 311 and the shaft portion 321. Moreover, theformation length Lsh of each of the hole-side strong press-fit portion314 and the shaft-side strong press-fit portion 324 is set according tothe bonding force between the hole 311 and the shaft portion 321, thebonding force being necessary for the joint component 300. Moreover, thesame second strong press-fit interference Ls2 forming the hole-sidestrong press-fit portion 314 and the shaft-side strong press-fit portion324 is applied.

As in the first embodiment, the first member 310 and the second member320 configured as described above are, as illustrated in FIG. 8,configured such that the second member 320 is arranged on a second die202 through a first step and a second step. Further, the first member310 is arranged on the second member 320. In this case, the first member310 is formed with such a small diameter that the shaft-side weakpress-fit portion 322 does not contact the hole-side weak press-fitportion 312 to ensure the second weak press-fit interference Lw2 betweenthe shaft-side weak press-fit portion 322 and the hole-side strongpress-fit portion 314. Thus, the first member 310 is arranged in a statein which the hole-side weak press-fit portion 312 is fitted at aposition facing the outside of the shaft-side weak press-fit portion322.

Then, a worker press-fits, as a third step, the hole-side weak press-fitportion 312 of the first member 310 and the shaft-side strong press-fitportion 324 of the second member 320 to each other. At the same time,the worker press-fits the hole-side strong press-fit portion 314 of thefirst member 310 and the shaft-side weak press-fit portion 322 of thesecond member 320 to each other. Specifically, the worker operates aprocessing machine 200 to move (move downward in a direction indicatedby a dashed arrow in FIG. 9) a first die 201 toward the second die 202in a non-current-application state. Accordingly, as illustrated in FIG.10, the hole-side weak press-fit portion 312 of the hole 311 of thefirst member 310 is fitted in the shaft-side strong press-fit portion324 of the shaft portion 321 of the second member 320. At the same time,the shaft-side weak press-fit portion 322 of the shaft portion of thesecond member 320 is fitted in the hole-side strong press-fit portion314 of the hole 311 of the first member 310. In this case, the firstmember 310 and the second member 320 are configured such that the secondweak press-fit interference Lw2 is set to such a thickness that no burrsare generated between these members, and therefore, are fitted to eachother with no burrs between both members.

At the third step, the first die 201 and the second die 202 each pressthe first member 310 and the second member 320 with these members beingdisplaceable in the radial direction. Thus, in a case where thepositions of the center axes of the hole-side weak press-fit portion 312and the shaft-side strong press-fit portion 324 are shifted from eachother upon fitting therebetween and the positions of the center axes ofthe shaft-side weak press-fit portion 322 and the hole-side strongpress-fit portion 314 are shifted from each other upon fittingtherebetween, at least one of the first member 310 or the second member320 is displaced in the radial direction such that the positions of thecenter axes of these members are coincident with each other. In thismanner, the first member 310 and the second member 320 are fitted toeach other with the center axes being coincident with each other. Thethird step corresponds to a second weak press-fit step according to thepresent invention. That is, each of the hole-side weak press-fit portion312 and the shaft-side weak press-fit portion 322 corresponds to a weakpress-fit portion according to the present invention. Each of thehole-side strong press-fit portion 314 and the shaft-side strongpress-fit portion 324 corresponds to a strong press-fit portionaccording to the present invention.

Next, the worker press-fits, as a fourth step, the hole-side strongpress-fit portion 314 of the first member 310 and the shaft-side strongpress-fit portion 324 of the second member 320 to each other.Specifically, the worker operates the processing machine 200 to move(move downward in a direction indicated by a dashed arrow in FIG. 10)the first die 201 toward the second die 202 in a current applicationstate between the first die 201 and the second die 202. Thus, asillustrated in FIG. 11, the hole-side strong press-fit portion 314 ofthe hole 311 of the first member 310 is fitted in the shaft-side strongpress-fit portion 324 through the gradually-changing portion 323 of theshaft portion 321 of the second member 320. Then, solid phase bondingbetween the hole-side strong press-fit portion 314 and the shaft-sidestrong press-fit portion 324 is made by resistance heat by applying acurrent and pressure due to lowering of the first die 201.

In this case, burrs B due to solid phase bonding between the hole-sidestrong press-fit portion 314 and the shaft-side strong press-fit portion324 might be generated at both end portions of a bonding portion SPbetween the hole 311 and the shaft portion 321. That is, the burrs B areor are not generated according to the formation length Lwh of each ofthe hole-side weak press-fit portion 312 and the shaft-side weakpress-fit portion 322.

At the bonding portion SP, a press-fit portion between the hole-sideweak press-fit portion 312 and the shaft-side strong press-fit portion324 and a press-fit portion between the shaft-side weak press-fitportion 322 and the hole-side strong press-fit portion 314 are eachbonding portions formed by press-fit bonding and/or solid phase bonding.A press-fit portion between the hole-side strong press-fit portion 314and the shaft-side strong press-fit portion 324 is a bonding portion bysolid phase bonding. In this case, the press-fit portion between thehole-side weak press-fit portion 312 and the shaft-side strong press-fitportion 324 and the press-fit portion between the shaft-side weakpress-fit portion 322 and the hole-side strong press-fit portion 314includes, according to the materials, shapes, press-fit conditions, andcurrent application conditions of the first member 310 and the secondmember 320, the case of bonding only by press-fitting, the case ofbonding only by solid phase bonding, and the case of bonding by acombination of press-fit bonding and solid phase bonding.

Thus, according to the joint component manufacturing method of thepresent invention, the formation length Lwh of each of the hole-sideweak press-fit portion 312 and the shaft-side weak press-fit portion 322and the formation length Lsh of each of the hole-side strong press-fitportion 314 and the shaft-side strong press-fit portion 324 are adjustedas necessary so that the amount of generated burrs B and bondingstrength between both members can be adjusted.

By the fourth step, the first member 310 and the second member 320 arebonded to each other to form the joint component 300. The fourth stepcorresponds to a second strong press-fit step according to the presentinvention. That is, each of the hole-side strong press-fit portion 314and the shaft-side strong press-fit portion 324 corresponds to a strongpress-fit portion according to the present invention.

Note that the bonding portion SP does not clearly appear, and FIG. 11merely illustrates trend. Moreover, in the second embodiment, the workerinstructs the processing machine 200 to execute each of the third andfourth steps. However, the processing machine 200 can be configured tocontinuously execute the third step and the fourth step by a singleinstruction. Thereafter, the worker takes, as a fifth step, the jointcomponent 300 out of the processing machine 200.

As seen from operation description above, in the joint componentmanufacturing method, the hole 311 of the first member 310 and the shaftportion 321 of the second member 320 are, according to the secondembodiment, bonded to each other by press-fitting with the second strongpress-fit interference Ls2 through press-fitting with the second weakpress-fit interference Lw2. In the this case, the second weak press-fitinterference Lw2 is, with respect to the second strong press-fitinterference Ls2, formed such that an overlapping thickness (i.e., thepress-fit interference) between both members is decreased. Thus,according to the joint component manufacturing method according to thepresent invention, occurrence of burrs in bonding between the firstmember 310 having the hole 311 and the second member 320 having theshaft portion 321 is reduced while close contact between both memberswithout any clearances and firm bonding between both members can berealized.

Further, implementation of the present invention is not limited to eachof the above-described embodiments, and various changes can be madewithout departing from the object of the present invention. Note thatthe same reference numerals are used to represent the same components asthose of each of the above-described embodiments in the figures referredin description of variations below, and description thereof will beomitted as necessary.

For example, in each of the above-described embodiments, a cornerportion of a tip end portion (an opening) on an insertion side of theshaft portion 121, 321 at the hole 111, 311 of the first member 110, 310and a corner portion of a tip end portion on an insertion side of thehole 111, 311 at the shaft portion 121, 321 of the second member 120,320 are formed at right angle. However, a guide portion 400 having aninclined surface or a curved surface can be provided at at least one ofthe corner portion of the tip end portion (the opening) of the hole 111,311 or the corner portion of the tip end portion of the shaft portion121, 321. For example, as illustrated in FIG. 12, the guide portion 400can be provided in an inclined surface shape at a corner portion of atip end portion of the shaft portion 121 on a side to be first fitted.In this case, the guide portion 400 is formed such that the outerdiameter of the shaft portion 121 increases from the tip end portion ofthe shaft portion 121 to a far side (the downward direction as viewed inFIG. 12) in the axial direction.

Alternatively, the guide portion 400 can be, for example, provided in acurved shape at a corner portion of a tip end portion of the hole 111 ona side to be first fitted, as illustrated in FIG. 13. In this case, theguide portion 400 is formed such that the inner diameter of the hole 111decreases from the tip end portion (an opening) of the hole 111 to thefar side (the upward direction as viewed in FIG. 13) in the axialdirection. In these cases, it is further effective that the length ofthe guide portion 400 in the axial direction is formed longer than thoseof the hole 111, 311 and the shaft portion 121, 321 in the radialdirection. With this configuration, the shaft portion 121, 321 of thesecond member 120, 320 is smoothly guided into the hole 111, 311 of thefirst member 110, 310, and therefore, is easily fitted in the hole 111,311. Thus, occurrence of burrs can be more effectively reduced.

In other words, this means that the first weak press-fit interferenceLw1 and the second weak press-fit interference Lw2 can be increased.According to the experiment by the present inventor et al., it has beenconfirmed that the guide portion 400 is provided at the corner portionof the tip end portion (the opening) of the hole 111 and occurrence ofburrs can be accordingly avoided even in a case where the first weakpress-fit interference Lw1 and the second weak press-fit interferenceLw2 have a diameter of greater than 0 mm and equal to or less than 0.2mm when the diameter of each of the hole 111 and the shaft portion 121formed of the steel members is within a range of 10 mm to 100 mm interms of diameter.

Moreover, in each of the above-described embodiments, thegradually-changing portions 123, 313, 323 are provided at the firstmember 310 and the second member 120, 320. However, the first member 310and the second member 120, 320 can be configured such that thegradually-changing portions 123, 313, 323 are omitted. In this case, atthe first member 310 and the second member 120, 320, the hole-side weakpress-fit portion 312 and the hole-side strong press-fit portion 314 arein a shape of which inner or outer diameter promptly changes in astepwise manner, and the shaft-side weak press-fit portion 122, 322 andthe shaft-side strong press-fit portion 124, 324 are in a shape of whichinner or outer diameter promptly changes in a stepwise manner.

Further, in each of the above-described embodiments, the first member110, 310 and the second member 120, 320 are made of the same material.However, the first member 110, 310 and the second member 120, 320 can bemade of different materials. In this case, at the first member 110, 310and the second member 120, 320, a member (e.g., a shape having arelatively-small thickness) in a more-deformable shape at the first weakpress-fit step and the second weak press-fit step is made of a materialhaving lower hardness than that of a member (e.g., a shape having arelatively-great thickness) in a less-deformable shape. Thus, occurrenceof the burrs B at the first weak press-fit step and the second weakpress-fit step can be more effectively reduced.

In addition, in each of the above-described embodiments, the first die201 and the second die 202 each press or support the first member 110,310 and the second member 120, 320 in a deformable state in thedirection perpendicular to the fitting direction. However, the first die201 and the second die 202 can also each press or support the firstmember 110, 310 and the second member 120, 320 in a state in whichdisplacement in the direction perpendicular to the fitting direction isrestricted, i.e., a state in which the first member 110, 310 and thesecond member 120, 320 are held.

Moreover, in each of the above-described embodiments, the processingmachine 200 is configured such that the first die 201 moves toward oraway from the second die 202. However, the processing machine 200 can beconfigured such that the second die 202 moves toward or away from thefirst die 201. Alternatively, the processing machine 200 can beconfigured such that the tops and bottoms of the first die 201 and thesecond die 202 are inverted. That is, in the joint componentmanufacturing method, the first member 110, 310 may be displaced withrespect to the second member 120, 320, or the second member 120, 320 maybe displaced with respect to the first member 110, 310. Displacement ofboth members is relative displacement.

LIST OF REFERENCE NUMERALS

-   Lw1 first weak press-fit interference-   Ls1 first strong press-fit interference-   Lw2 second weak press-fit interference-   Ls2 second strong press-fit interference-   Lwh formation length of weak press-fit portion-   Lsh formation length of strong press-fit portion-   ST bonding thickness-   SP bonding portion-   B burr-   100, 300 joint component-   110, 310 first member-   111, 311 hole-   112, 312 hole-side weak press-fit portion-   313 gradually-changing portion-   314 hole-side strong press-fit portion-   120, 320 second member-   121, 321 shaft portion-   122, 322 shaft-side weak press-fit portion-   123, 323 gradually-changing portion-   124, 324 shaft-side strong press-fit portion-   200 processing machine-   201 first die-   202 second die-   400 guide portion

The invention claimed is:
 1. A joint component manufacturing method forjoining a first member and a second member by fitting of a shaft portionof the second member in a hole of the first member, the first member andthe second member each including a weak press-fit portion at a tip endportion, the tip end portion of the first member and the tip end portionof the second member first fitted to each other upon fitting between thehole and the shaft portion, and the first member or the second memberincluding a strong press-fit portion formed to protrude to a far side ofthe tip end portion, the method comprising: a first weak press-fit stepof press-fitting the weak press-fit portion of the first member and theweak press-fit portion of the second member in a non-current-applicationstate; and a first strong press-fit step of press-fitting the strongpress-fit portion and either one of the weak press-fit portion of thefirst member or the weak press-fit portion of the second member in astate in which electric resistance heat is generated between the firstmember and the second member by applying a current, wherein a first weakpress-fit interference, which is a thickness of an overlapping portionupon fitting between the weak press-fit portion of the first member andthe weak press-fit portion of the second member, is thinner than a firststrong press-fit interference, which is a thickness of an overlappingportion upon fitting between the strong press-fit portion and either oneof the weak press-fit portion of the first member or the weak press-fitportion of the second member.
 2. The joint component manufacturingmethod according to claim 1, wherein the first weak press-fitinterference is formed to such an overlapping thickness that no burr isgenerated between the first member and the second member fitted to eachother.
 3. The joint component manufacturing method according to claim 1,wherein a guide portion having an inclined surface or a curved surfaceis formed at at least one corner portion of the tip end portions firstfitted to each other upon fitting between the hole and the shaftportion.
 4. The joint component manufacturing method according to claim1, wherein at least one of the weak press-fit portion of the firstmember or the weak press-fit portion of the second member has anarc-shaped gradually-changing portion of which the shape graduallychanges with respect to the strong press-fix portion.
 5. The jointcomponent manufacturing method according to claim 1, wherein at leastone of the weak press-fit portion of the first member or the weakpress-fit portion of the second member is formed to be uniform with eachof an inner diameter of the hole and an outer diameter of the shaftportion.
 6. The joint component manufacturing method according to claim1, wherein a length of at least one of the weak press-fit portion of thefirst member or the weak press-fit portion of the second member in anaxial direction is formed to be equal to or less than ½ of a length ofthe strong press-fix portion in an axial direction.
 7. The jointcomponent manufacturing method according to claim 1, wherein a length ofat least one of the weak press-fit portion of the first member or theweak press-fit portion of the second member in an axial direction isformed to be equal to or greater than ⅕ of a thickness of a bondingportion between the hole and the shaft portion.